Fuser roll assembly

ABSTRACT

A fuser roll assembly for use in a xerographic copying machine including a cylindrical roll formed of aluminum and having an electric heating element disposed along its longitudinal axis. A substantially cylindrical shell, formed of stainless steel, is slidably mounted about the roll when the heating element is deenergized; energization of the heating element causing said roll to diametrally expand so the outer surface of the roll firmly engages the inner surface of the shell.

[ 1 Aug.7, 1973 United States Patent i 91 Gregory FUSER ROLL ASSEMBLY 219/469 263/6 E Brownscombe..................... 219/469 Kesten o 022 777 999 HHH 26 874 208 9 7 0 0092 463 333 Ilg [73] Assignee: Xerox Corporation, Stamford,

Primary Examiner-John J Camby Assistant Examiner Conn.

Henry C. Yuen 22 Filed: N 2 1971 Azt0 rney.lames .1. Ralabate et a1.

[21] Appl. No.: 202,495

[57] ABSTRACT A fuser roll assembly for use in a xerographic copying machine including a cylindrical roll formed of aluminum and having an electric heating element disposed along its longitudinal axis. A substantially cylindrical shell, formed of stainless steel, is slidably mounted 2HN Q52: m 4 0 6 0 69" fi m 3 m 2 m Mmm 21 4 I. C QM 1 U h 1 l 2 .l 5 5 [58] Field of Search................. 263/6 C, 6 E; 355/8; 219/469, 216; 432/60, 62, 227, 228

about the roll when the heating element is deenergized; energization of the heating element causing said roll to diametrally expand so the outer surface of the roll firmly engages the inner surface of the shell.

4 Claims, 1 Drawing Figure 99 66 44 WWW 116 222 Flanagan. 219/216 4/1969 Manghirmalani et al.

3,586,827 6/1971 3,637,976 l/l972 Ohta et al.

3,449,548 1/1969 Adamek et a1...

Pmmmw 1 INVENTOR PAUL M. GREGOR Y L44 M Zrromvsr v FUSER ROLL ASSEMBLY BACKGROUND OF THE INVENTION This invention relates in generalto the fixing of developed latent electrostatic images on a substrate, and more particularly, to apparatus for obtaining the desired permanent bondingof toner material, employed for development purposes in a xerographic copying machine, to the substrate.

In an automatic xerographic process of a type familiar to those skilled in the art and exemplified by US. Pat. No. 3,062,108, issued in the name of Clyde R. Mayo, the utilization of. a heated fixing mechanism for achieving, the permanent bonding of the developed latent electrostatic image onto the copy medium has proven highly satisfactory. Onesuch fixing mechanism is commonly referred to as a fuser roll assembly. The fuser roll assembly additionally functions to feed the copy medium, such as paper, through the transfer station of the typical xerographic process. In providing the foregoing function, the fuser roll assembly cooperates with a backup roll. An example of such fuser roll assembly is disclosedin U.S'. Pat. No. 3,291,466 issued to Aser etal. I

In a typical construction of'a fuser roll assembly, a hollow, generally cylindricaliroll is mounted for rotation about its longitudinal axis, and is provided, along this axis, with an electric heating element. Such a roll is usually constructed of copper or aluminum and is provided-with-a coatingof a suitable thermoplastic material, for example, polytetrofluroethylene hereinafter referred to as PTFE). PTFE is-a fluorocarbon resin cur.- rently soldunder the trademark Teflon by the E. I. duPont de Nemours and Company, Inc.

In operation, fuser roll assemblies are subjected to relatively high temperaturesand:pressures and this, together with manufacturing difficulties in obtaining perfect adhesion of the PTFE to the surface of the assembly roll, is the cause of deterioration of the PTFE coating which makesthe roll unsatisfactory for continued use, thus necessitating its replacement. Where the roll is formed of copper, the roll is returned from the field,

" the PTFE being thereafter machined off (PTFE being .almost chemically inert cannot be stripped easily without machining back to the. base material). This machining operation causes'loss ofdiameter beyond diameter tolerances, so the roll is deliberately machined about 0.025 inches below true diameter and then built up oversize again, as by spraying with aluminum. The roll is then machined again to true diameter, and coated with PTFE asan'original roll.

Thisis a costly and tedious process.

When the roll is formed of aluminum, which is less expensive than copper, it is found economical to discard the aluminum rolls entirely when they can no longer be-sa tisfactorilyv employed in copying machines. New roll assembliesare then substituted for the discarded assemblies. The difference in initial material costs plu's the elimination of shipping costs from the field to the fuser assembly renovation site approximates the cost of repairingfuser roll assemblies including copperrolls. It isapparentthat neither of these repair methods-for fuser roll assemblies is satisfactory.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide fuser roll assemblies that may be readily repaired at minimal cost.

It is a further object of the invention to provide a fuser roll assembly that may be repaired at the installation site of the copying machine in which the assembly is employed. I

It is a further object to provide a fuser roll assembly that is less expensive to manufacture and to repair, and one that will require less maintenance.v

These and other objects of the invention are obtained by forming the fuser roll assemblyin a unique manner. The assembly in accordance with the invention includes a cylindrical roll, which functions as the assembly core, having an electrical heating element disposed along its longitudinal axis. A substantially cylindrical shell is slidably mounted about the roll while the heating element is deenergizedf The roll is thereafter expanded diametrally relative to the shell so the outer surface of the rollfirmly engages the inner surface of the shell. The shell preferably, has a coating of PTFE disposed thereabout.

In a preferredembodiment of the invention, the core andthe shell are ofsuch materials that at room temperatures, the shell is slidable over the" core, whereas when the heating element is. energized so the assembly achieves its normal operating temperature, the core expands diametrally more than the shell. Preferably, the core is of aluminum and'the shell is of stainless steel.

In an alternative embodiment, for example, inja case where it is desired to use other materials for the core and shell, the core may be provided with a conventional mechanical expansion device.

By employing the fuser roll assembly of the present invention, when the shell is worn, it may be removed (when the roll is at room temperature or when the expansion device iscontracted) and thereafter discarded. A new shell may then be positioned concentrically about the core and spaced apart from the core; the core expanding to grip the shell tightly as the roll is brought up to its operating temperatures, or as the expansion device is expanded.

Other objects of the invention and further features thereof shall become apparent to those skilled in the art in view of the following detailed disclosure and description of a preferred embodiment of the invention, particularly' when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE of the drawing shows a sectioned perspective view of a fuser roll assembly as contemplated by the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT flurocarbon resin, such as PTFE.

A typical operating temperature for a fuser roll assembly of this kind when element 3 is energized, is about 365 F, and at such a temperature, the aluminum roll 1 expands outwardly so the outer surface thereof firmly grips the inside surface of shell 4. The foregoing occurs due to the fact that the coefficient of thermal expansion for aluminum is greater than is the coefficient of thermal expansion for stainless steel.

When a shell is worn, it may easily be replaced, and the worn-out shell discarded. In the preferred embodiment, the shell is removed from the assembly when element 3 is deenergized; shell 4 being thus slidable relative to roll 1. Such a fuser roll assembly has the advantages that it is relatively inexpensive to produce when compared to fuser roll assemblies heretofore known (about half the cost of an assembly including an aluminum roll, and about a quarter of the cost of an assembly including a copper roll). Additionally, the adhesion of the PTFE, as proved by experiments, is likely to be more reliable on stainless steel than on copper or aluminum, thus giving longer field life. Furthermore, the PTFE coating time is greatly reduced, because the thin shells in bulk do not cause curing-oven temperature drop as is now experienced with the considerable mass of conventional rolls. Further, the costly and tedious repairs heretofore necessitated for conventional fuser roll assemblies are hereby eliminated.

While the present invention is carried out in a specific embodiment, it is not intended to be limited thereby but it is intended to be covered broadly within the scope of the appended claims.

What is claimed is:

l. A fuser roll assembly for use in a xerographic copying machine, including:

a cylindrical roll member of a first material having a first coefficient of thermal expansion and being mounted for rotation about its longitudinal axis,

heating means disposed along the longitudinal axis of said roll member for supplying heat thereto, said heating means 'being energizable and deenergizable as desired to control the temperature of said roll member,

a hollow cylindrical shell member of a second material having a second and lower coefficient of then mal expansion, said shell member being rotatably and translatably disposable around said roll member when said roll member is at room temperature and being securely engaged by said roll member when said rollmember is at operating temperature.

2. A fuser roll assembly as defined in claim 1 wherein said roll member is composed substantially of aluminum and said shell member is composed substantially of stainless steel.

3. The fuser roll assembly in accordance with claim 1 wherein said shell is provided with a coating of a flurocarbon resin.

4. A fuser roll assembly for copying machine comprising: I I

a generally cylindrical roll member formed of aluminum,

heating means disposed along the longitudinal axis of said roll for supplyingheat thereto, and

a substantially cylindrical shell member formed of stainless steel and having a'flu'rocarbon resin coating provided on its outer surface, said shell member being slidably mounted about said roll member when said heating means is deenergized, energization of said heating means causing said roll member to diametrally expand so the outer surface thereof firmly engages the inner surface of said shell member.

use in a xerographic 

1. A fuser roll assembly for use in a xerographic copying machine, including: a cylindrical roll member of a first material having a first coefficient of thermal expansion and being mounted for rotation about its longitudinal axis, heating means disposed along the longitudinal axis of said roll member for supplying heat thereto, said heating means being energizable and de-energizable as desired to control the temperature of said roll member, a hollow cylindrical shell member of a second material having a second and lower coefficient of thermal expansion, said shell member being rotatably and translatably disposable around said roll member when said roll member is at room temperature and being securely engaged by said roll member when said rollmember is at operating temperature.
 2. A fuser roll assembly as defined in claim 1 wherein said roll member is composed substantially of aluminum and said shell member is composed substantially of stainless steel.
 3. The fuser roll assembly in accordance with claim 1 wherein said shell is provided with a coating of a flurocarbon resin.
 4. A fuser roll assembly for use in a xerographic copying machine comprising: a generally cylindrical roll member formed of aluminum, heating means disposed along the longitudinal axis of said roll for supplying heat thereto, and a substantially cylindrical shell member formed of stainless steel and having a flurocarbon resin coating provided on its outer surface, said shell member being slidably mounted about said roll member when said heating means is deenergized, energization of said heating means causing said roll member to diametrally expand so the outer surface thereof firmly engages the inner surface of said shell member. 